The irrigation sector claims about 70 percent of the freshwater withdrawals worldwide. Irrigation can offer crop yields that are two to four times greater than is possible with rainfed farming, and it currently provides 40 percent of the world’s food from approximately 20 percent of all agricultural land.

Since the late 1970s, irrigation expansion has experienced a marked slowdown. The FAO attributes the decline in investment to the unsatisfactory performances of formal large canal systems, corruption in the construction process, and acknowledgement of the environmental impact of irrigation projects.

The increasing availability of inexpensive individual pumps and well construction methods has led to a shift from public to private investment in irrigation, and from larger to smaller-scale systems. The takeoff in individual groundwater irrigation has been concentrated in India, China, and much of Southeast Asia. The idea of affordable and effective irrigation is attractive to poor farmers worldwide, with rewards of higher outputs and incomes and better diets.

The option is often made even more appealing with offers of government subsidies for energy costs of running groundwater pumps and support prices of irrigated products. In India’s Gujarat state, for example, energy subsidies are structured so that farmers pay a flat rate, no matter how much electricity they use. But with rising numbers of farmers tapping groundwater resources, more and more aquifers are in danger of overuse.

If groundwater resources are overexploited, aquifers will be unable to recharge fast enough to keep pace with water withdrawals. It should be noted that not all aquifers are being pumped at unsustainable levels—in fact, 80 percent of aquifers worldwide could handle additional water withdrawals. One troubling aspect of groundwater withdrawals is that the world’s major agricultural producers (particularly India, China, and the United States) are also the ones responsible for the highest levels of depletion.

Another problem with pumping water from aquifers and redirecting flows for irrigation is the impact on delicate environmental balances. Salinization occurs when water moves past plant roots to the water table due to inefficient irrigation and drainage systems; as the water table rises, it brings salts to the base of plant roots.Plants take in the water, and the salts are left behind, degrading soil quality and therefore the potential for growth.

A potentially better alternative is drip irrigation, a form of micro-irrigation that waters plants slowly and in small amounts either on the soil surface or directly on roots.Using these techniques has the potential to reduce water use by as much as 70 percent while increasing output by 20–90 percent. Within the last two decades, the area irrigated using drip and other micro-irrigation methods has increased 6.4-fold, from 1.6 million hectares to over 10.3 million hectares.

With predictions of a global population exceeding 9 billion by 2050, demand for higher agricultural output will put more strain on already fragile water reserves. Even without the effects of climate change, water withdrawals for irrigation will need to rise by 11 percent in the next three decades to meet crop production demands.Reconciling increasing food demands with decreasing water security requires efficient systems that produce more food with less water and that minimize water waste. Intelligent water management is crucial especially in the face of climate change, which will force the agriculture industry to compete with the environment for water.

Further highlights from the report:

The share of the area equipped for irrigation that is actually under irrigation ranges from 77 to 87 percent in Asia, Africa, the Americas, and in Oceania, but is only 59 percent in Europe. More reliable rainfall allows farmers in northern and eastern Europe to rely less on existing irrigation infrastructure than is the case in drier or more variable climates.

Worldwide, the most commonly used irrigation technique is flood irrigation, even though plants often use only about half the amount of water applied in that system.

India claims the lead in irrigated area worldwide, irrigating almost 2 million hectares of its land using drip and micro-irrigation techniques.